International patent application publication WO 2011/062490 in the name of Levitech B.V. discloses a substrate processing apparatus including a process tunnel through which semiconductor substrates may be contactlessly advanced in rapid succession while being subjected to a variety of treatments such as, for example, spatial atomic layer deposition (ALD) and annealing. A problem addressed in WO'490 is that the substrates, which are floatingly supported between an upper and lower gas bearing, may become destabilized by gas flows necessary to maintain the gas bearings. Consequently, the substrates may stray from their predetermined trajectory towards the edges of the gas bearings and/or undergo angular displacements, as a result of which they may collide with and/or get stuck between the walls bounding the process tunnel. Although the lateral stabilization mechanism proposed by WO'490 works satisfactorily in significantly reducing the occurrence rate of such events, practice has taught that substrate-wall contacts may not be prevented entirely.
In the event that a substrate-wall contact involves fracture of the substrate and/or congestion of the process tunnel, quick and convenient access to the tunnel space is desired in order to enable operators to remedy the situation and to effect prompt resumption of the production process. The same applies, of course, in case a substrate fractures or gets stuck for other reasons. In practice, for instance, a substrate may already be slightly damaged upon insertion into the process tunnel. If such a substrate is then rapidly heated as part of a (pre-)anneal treatment, the thermal expansion of the cracked substrate may cause it to break into pieces.